ViewState Deserialization Zero-Day Vulnerability in Sitecore Products (CVE-2025-53690)

Written by: Rommel Joven, Josh Fleischer, Joseph Sciuto, Andi Slok, Choon Kiat Ng Update (September 3): This post was updated to include information about GoTokenTheft usage. In a recent investigation, Mandiant Threat Defense discovered an active ViewState deserialization attack affecting Sitecore deployments leveraging a sample machine key that had been exposed in Sitecore deployment guides from 2017 and earlier. An attacker leveraged the exposed ASP.NET machine key to perform remote code execu